The structure, function and development of the granulosa layer in lizards with special reference to Scincus mitranus (Anderson)

Al-Doky, Othman A.I (1989) The structure, function and development of the granulosa layer in lizards with special reference to Scincus mitranus (Anderson). University of Southampton, Doctoral Thesis.

Abstract

Following a review of previous work on the granulosa layer the thesis deals mainly with the structure of the developing follicle in the lizard Scincus mitranus. Comparison of the granulose of this species with that of Podarcis muralis indicates that the large cells of the skink are, because of their size, possibly more suited to the study of granulosa cell structure and function than species previously investigated.

The feasibility of using S. mitranus for the study of granulosa cell structure and function was established by a study of the reproductive cycle based mainly on field observations.

After a general survey of ovarian structure the development of the granulosa layer and the accompanying growth of the oocyte during the pre-vitellogenic stage of oogenesis is described in detail. The previtellogenic stage was of primary interest since it is during this stage that the conspicuously large granulosa cells attain their greatest structural complexity and presumably functional activity. The large granulosa cells of S. milranus are probably the largest among lizards species which have been studied so far. They measure up to 35 fim 'n width and up to 80 /im in length; also

in contrast to the majority of lizards species they do not posses a pyriform shape, instead they flatten over the oocyte surface in an obloid shape.

A detailed ultra structural investigation of the granulosa cells gives some indication of their relationship to each other and to the possible contribution of the large cells to the growth of the associated oocyte. Initially the large cells establish a microvillus connection with the oocyte (during the transitional stage), subsequently a single cytoplasmic bridge appears to be established between each large cell and the adjacent ooctye interface. Subsequently large cell degeneration is observed, accompanied by a great increase in lipid content of the large cells. As degeneration proceeds the large cells appear to expel their contents into the oocyte before they completely disappear and the granulosa layer reverts to a single layer of small cells.

Methods used to preserve lipids and detect cholesterol and phospholipid gave some indication that lipid/cholesterol and phospholipid transfer to the ooctye is a significant function of the large cells.

A quantitative study of granulosa cell number and size in relation to the growing oocyte indicates that only a relatively small proportion of the initial population of small cells gives rise to intermediate and large cells.

Finally the main findings of the thesis are assessed and discussed in relation to previous work.

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